/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/ViewModels/HierarchyEditor/NiagaraUserParametersHierarchyViewModel.h
The hierarchy root the widget is editing. This should point to persistent data stored somewhere else as the serialized root of the hierarchy.
virtual [UNiagaraHierarchyRoot](API\Plugins\NiagaraEditor\ViewModels\HierarchyEditor\UNiagaraHierarchyRoot) * GetHierarchyRoot() const